1. Field of the Invention
The present invention relates to a rotation angle detection device used for detecting a rotation angle of a steering wheel of an automobile and the like.
2. Background Art
Recently, functions of an automobile have been enhanced. In such circumstances, automobiles using various rotation angle detection devices for detecting a rotation angle of a steering wheel and using this detected rotation angle to perform various controls of a vehicle have been increased.
Such a conventional rotation angle detection device is described with reference to FIGS. 4 and 5. FIG. 4 is a partial sectional view showing a conventional rotation angle detection device, and FIG. 5 is an exploded perspective view showing a conventional rotation angle detection device. In FIGS. 4 and 5, spur gear 111 is formed on the outer side surface of rotary body 101. Engaging part 112, which is engaged with a steering shaft (not shown) to be inserted, is provided at the center part of rotary body 101.
Spur gear 121 is formed on the outer side surface of first detector 102. Spur gear 131 is formed on the outer side surface of second detector 103. Spur gear 131 has a different number of cogs from that of spur gear 121. Spur gear 121 of first detector 102 meshes with spur gear 111 of rotary body 101. Furthermore, spur gear 131 of second detector 103 meshes with spur gear 121 of first detector 102.
Furthermore, wiring board 104 is disposed above first detector 102 and second detector 103 substantially in parallel thereto. A plurality of wiring patterns (not shown) is formed on the upper and lower surfaces of wiring board 104. Furthermore, magnetic detection elements 161 and 162 are placed on wiring board 104, respectively. Magnet 151 placed at the center of first detector 102 faces magnetic detection element 161. Magnet 152 placed at the center of second detector 103 faces magnetic detection element 162.
Thus, magnet 151 and magnetic detection element 161, which face each other, form a first detection part. Similarly, magnet 152 and magnetic detection element 162, which face each other, form a second detection part. Furthermore, wiring board 104 includes control part 107 coupled to magnetic detection elements 161 and 162 by an electronic component such as a microcomputer.
Furthermore, case 108 has a substantially box-shape and is made of insulating resin. Rotary body 101 is rotatably held in through-hole 181 of case 108. First detector 102 is rotatably held in hollow cylindrical part 182. Second detector 103 is rotatably held in hollow cylindrical part 183.
Furthermore, cover 109 has a substantially box-shape and is made of insulating resin. Cover 109 covers an opening part on the upper surface of case 108. Rotary body 101, first detector 102 and second detector 103 are rotatably held between case 108 and cover 109. Wiring board 104 is fixed and held to cover 109. Case 108 and cover 109 are coupled to each other with a plurality of screws 110. Thus, a conventional rotation angle detection device is configured.
In the thus configured rotation angle detection device, control part 107 is coupled to an electronic circuit of an automobile (not shown) via a connector, a lead wire (not shown), or the like. Furthermore, a steering shaft (not shown) is inserted in engaging part 112 of rotary body 101 to be placed on an automobile.
In the above-mentioned configuration, when a steering wheel is rotated, rotary body 101 latched onto a steering shaft is rotated. First detector 102 is rotated in linked motion with rotary body 101. Second detector 103 is rotated in linked motion with first detector 102. Therefore, magnets 151 and 152 placed respectively in the center of first and second detectors 102 and 103 are also rotated. Magnetic detection elements 161 and 162 detect the change in the magnetism of magnets 151 and 152 as a detection signal, respectively. At this time, the data waveforms of magnetic detection elements 161 and 162 are detection signals differing in cycle and phase from each other because the numbers of cogs are different and rotation speeds are also different between first detector 102 and second detector 103.
Then, control part 107 detects a rotation angle of rotary body 101, that is, a rotation angle of the steering wheel by executing a predetermined operation according to the two different detection signals and the numbers of cogs of first detector 102 and second detector 103. This detected rotation angle is output to an electronic circuit of an automobile, so that various controls of a vehicle are carried out.
During the above-mentioned rotation operation, first detector 102 and second detector 103 are rotated in a state in which they are held in hollow cylindrical parts 182 and 183 of case 108, respectively. However, in the manufacture of a device, when wiring board 104 fixed to cover 109 is fabricated into case 108 and cover 109 in a state in which it is displaced, a center displacement occurs between magnets 151, 152 of first and second detectors 102, 103 held in case 108 and magnetic detection elements 161, 162 placed on wiring board 104.
Furthermore, case 108, cover 109 and wiring board 104 are made of different materials and have different shapes from each other. Therefore, amounts of expansion or shrinkage differ from each other depending upon the temperature and humidity of the environment in which the device is used, in particular, when the device is used at high or low temperature. As a result, a center displacement is increased between magnet 151 and magnetic detection element 161, or between magnet 152 and magnetic detection element 162.
Such a center displacement occurring between magnet 151 and magnetic detection element 161 or between magnet 152 and magnetic detection element 162, when the device is fabricated or used at high or low temperature, is actually from about 0.1 to 0.5 mm. However, such a displacement causes an error in the magnetism of magnets 151 and 152 detected by magnetic detection elements 161 and 162. As a result, a rotation angle detected by control part 107 based on a predetermined operation may include an angle error of about 1° to 2°.
In this way, in the above-mentioned conventional rotation angle detection device, magnets 151 and 152 are placed in first and second detectors 102 and 103 which are held in case 108, respectively. Furthermore, magnetic detection elements 161 and 162 are placed on wiring board 104 fixed to cover 109, respectively. Therefore, when the device is fabricated or used at high or low temperature, the center displacement may occur between magnet 151 and magnetic detection element 161 or between magnet 152 and magnetic detection element 162, respectively. As a result, a detection error of a rotation angle may occur.
Note here that the prior art technique related to the invention of the present application is shown in, for example, Japanese Patent Unexamined Publication No. 2006-258625.